Vaughan (1978:39-40) included this family in Pongidae (which is here considered a part of Hominidae); but see Delson and Andrews (1975:441) and Thenius (1981). Szalay and Delson (1979:461), McKenna and Bell (1997), and Goodman et al. (1998) included Hylobatidae in Hominidae. The family is usually awarded a single genus (Hylobates), which is divided into four subgenera, but Groves (2001c:289) and Roos and Geissmann (2001) considered that they should probably be elevated to full genera, but Groves (2001c) did not take this final step because of the nomenclature problem of Bunopithecus. It seems, however, undesirable that a problem of nomenclature should be allowed to obstruct a desirable taxonomic change. Goodman et al. (1998) separated Symphalangus and Hylobates as full genera (they had no material for the other two genera/subgenera).